1. Field of the Invention
The present invention relates to lube oil compositions for diesel engines, and more particularly to lube oil compositions suitable for use as cylinder oils for two-cycle marine engines.
2. Description of the Related Art
Fuels used for diesel engines generally have high sulfur content, and therefore, exhaust gases from diesel engines contain large amounts of sulfur oxides (hereinafter collectively referred to as SOx). SOx reacts with moisture which is also present in exhaust gases to form sulfuric acid, which breaks an oil film of a lube oil for diesel engines and corrodes or wears components of the diesel engine. Particularly in the case of two-cycle marine engines, corrosion and wear of cylinder liners or piston rings raise serious problems. Therefore, lube oils for diesel marine engines must have properties that can effectively prevent corrosion and wear. To this end, conventional lube oils for diesel engines (hereinafter maybe referred to as diesel engine oils) have been designed to include metallic detergents/dispersants of the over based type, to thereby neutralize sulfuric acid that has been produced.
With a recent trend of increased popularity of diesel engines for land vehicles which are equipped with a unique system of circulating and recombusting exhaust gas (EGR, i.e., exhaust gas recirculation) for coping with exhaust gases, the SOx content of exhaust gases tends to increase. Also, in diesel marine engines, fuels of high sulfur content are widely used with an aim of cutting costs. However, this invites a tendency of increased SOx content as is the case with diesel engines for land vehicles.
As a conceivable measure for solving this problem, the amount of a over based metallic detergent/dispersant, which serves as a neutralizer, may be increased. However, the sole use of this approach cannot sufficiently neutralize and remove large amounts of sulfuric acid, and therefore, corrosion and wear cannot be fully prevented.
There has been tried another approach in which metallic detergents/dispersants are used in combination with a plurality of additives such as ashless dispersants to thereby promote the neutralizing effect of the metallic detergents/dispersants for acids, so as to prevent wear and corrosion of cylinder liners and piston rings. For example, Japanese Patent Application Laid-Open (kokai) No. 6-271885 discloses in its Example section additives containing Ca-salicylate and bis-type alkenylsuccinic imide. However, in order to promote the effect of neutralizing acid by use of the bis-type alkenylsuccinic imide, an amine molybdenum complex must be further added.
In this connection, the ability of diesel engine oils to prevent wear/corrosion of cylinder liners or piston rings can be assessed by measurement of the reaction rate of the lube oil to neutralize acids, because acid neutralization reaction rate is known to correlate with corrosion/wear of cylinder liners and piston rings.
The present invention has been made in view of the foregoing, and the object of the present invention is to provide a lube oil composition for diesel engines, which is endowed with excellent anticorrosion/antiwear properties even when used for diesel engines which exhaust large amounts of SOx.
The present inventors have conducted careful studies based on the aforementioned acid neutralization rate, and have found that when a specific type of over based alkaline earth metal compound is combined with a specific type of succinic imide compound, the object of the present invention can be effectively attained, leading to completion of the present invention.
Accordingly, the present invention is directed to a lube oil composition for diesel engines, which comprises a lube oil base having a kinematic viscosity of 8-35 mm2/s at 100xc2x0 C.; a component (A) which is at least one compound selected from the group consisting of over based sulfonates of alkaline earth metals, over based phenates of alkaline earth metals, and salicylates of over based alkaline earth metals; and a component (B) which is a bis-type succinic imide compound having an absorption ratio, xcex1/xcex2, of absorption peaks in an IR spectrum (wherein xcex1 is the intensity of an absorption peak at 1550xc2x110 cmxe2x88x921 and xcex2 is the intensity of an absorption peak at 1700xc2x110 cmxe2x88x921) of not more than 0.005.
The present invention also relates to a lube oil composition for diesel engines, which comprises component (A) in an amount of 5-40% by weight and component (B) in an amount of 0.1-3% by weight, both based on the total weight of the composition.
The present invention also relates to a lube oil composition for diesel engines, in which the total base number of the composition falls within the range from 30 to 150 mgKOH/g.
The present invention still further relates to a lube oil composition for diesel engines, wherein the concentration of the nitrogen atoms contained in the composition is 10-200 ppm by weight based on the total weight of the composition.
These and other objects, features, and advantages of the present invention will become apparent from the following description.
The present invention will next be described in detail.
The lube oil base of the lube oil composition of the present invention for diesel engines is a mineral oil and/or a synthetic oil having a kinematic viscosity of 8-35 mm2/s, preferably 10-25mm2/s. If the kinematic viscosity at 100xc2x0 C. is higher than 35 mm2/s, the fuel consumption rate becomes unsatisfactory, whereas if it is less than 8, the lube oil composition evaporates considerably, both cases being not preferable. There is no particular limitation as to the pour pointxe2x80x94which serves as an index for the low temperature fluidityxe2x80x94of the base oil. However, it is generally preferred that the pour point be not higher than xe2x88x9210xc2x0 C.
Several types of mineral oils and synthetic oils are usable in the present invention, and they are suitably selected in accordance with use, etc. Examples of mineral oils include, but are not limited to, paraffin base mineral oils, naphthene-type mineral oils, and intermediate-base-type mineral oils. Specific examples of mineral oils include light neutral oils, intermediate neutral oils, heavy neutral oils, and bright stocks.
Examples of synthetic oils include, but are not limited to, polyxcex1-olefin, xcex1-olefin copolymers, polybutene, alkylbenzene, polyol esters, dibasic acid esters, polyoxyalkylene glycols, polyoxyalkylene glycol esters, and polyoxyalkylene glycol ethers.
These base oils may be used singly or in combination of two or more species, and a mineral oil and a synthetic oil may be used in combination.
Components (A) and (B) which are incorporated into the lube oil base will next be described.
Component (A)
The component (A) of the present invention is a compound selected from the group consisting of over based sulfonates, phenates, and salicylates of alkaline earth metals. These compounds have conventionally been used as metallic detergents/dispersants. Preferable total base numbers of these compounds fall within the range from 100 to 600 mgKOH/g (JIS K-2501: perchloricacid method). Total base numbers of lower than 100 mgKOH/g require increased amounts of additives, and therefore are economically disadvantageous. On the other hand, if the total base number is in excess of 600 mgKOH/g, the ash content of the lube oil increases, raising the risk of producing great amounts of deposit during long-term use.
The over based sulfonates of alkaline earth metals that are usable as component (A) may usually be obtained through carbonation of alkaline earth metal salts of a variety of sulfonic acids. Examples of usable sulfonic acids include aromatic petrosulfonic acids, alkylsulfonic acids, arylsulfonic acids, and alkyl sulfonic acids. Specific examples of preferred over based sulfonates of alkaline earth metals include dodecylbenzenesulfonic acid, dilaurylcetylbenzenesulfonic acid, paraffin-wax-substituted benzenesulfonic acid, polyolefin-substituted benzenesulfonic acid, polyisobutylene-substituted benzenesulfonic acid, and naphthalenesulfonic acid.
More preferable over based sulfonates of alkaline earth metals include compounds of the following formulas (1) and (2): 
wherein each of R1 and R2, which may be identical to or different from each other, represents an alkyl group, preferably a C20-C30 alkyl group, and M represents an alkaline earth metal, which is preferably calcium, magnesium, or barium: 
wherein R1, R21 and M have the same meanings as defined in formula (1), and R3 represents an alkylene group, preferably a C10-C40 alkylene group, more preferably a C20-C30 alkylene group.
The over based phenatesxe2x80x94another type of compounds (A)xe2x80x94of alkaline earth metals are alkaline earth metal salts of an alkyl phenol or a sulfidized alkyl phenol. They are usually obtained through carbonation of alkaline earth metal salts of an alkyl phenol or a sulfidized alkyl phenol.
Examples of preferred over based phenates of alkaline earth metals include compounds of the following formulas (3) and (4): 
wherein each of R4 and R5, which may be identical to or different from each other, represents an alkyl group, preferably a C1-C20 alkyl group, more preferably a C5-C8 alkyl group, M represents an alkaline earth metal, preferably calcium, magnesium, or barium, and x is a positive number from 1 to 2; 
wherein R4, R5, M, and x have the same meanings as defined in formula (3).
The over based salicylatesxe2x80x94still another type of compounds (A)xe2x80x94of alkaline earth metals are alkaline earth metal salts of an alkyl salicylate. They are usually obtained by alkylating a phenol with C8-C18 xcex1-olefin, carrying out a Kolbe-Schmitt reaction to thereby introduce a carboxyl group, then a double decomposition, to complete carbonation.
More specifically, compounds of the following formula (5) may be used as the over based salicylates of a alkaline earth metal. 
wherein each of R6 and R7, which may be identical to or different from each other, represents an alkyl group, preferably a C10-C40 alkyl group, more preferably a C20-C30 alkyl group, M represents an alkaline earth metal, preferably calcium, magnesium, or barium, and x is a positive number from 1 to 2.
Specific examples of alkyl salicylates include dodecyl salicylate, dodecylmethyl salicylate, tetradecyl salicylate, hexadecyl salicylate, octadecyl salicylate, and dioctadecyl salicylate.
Alkaline earth metals for preparing sulfonates, phenates, and salicylates include calcium, magnesium, and barium. From the viewpoint of effect, calcium is preferred.
In the present invention, compound (A) may be used singly or in combination. It is preferably incorporated in an amount of 5-40% by weight, more preferably 10-30% by weight with respect to the total weight of the composition. Amounts less than 5% by weight may sometimes result in an insufficient acid neutralization effect, whereas amounts in excess of 40% by weight no longer produce appreciable effects commensurate with the amounts used.
Component(B)
Examples of ashless dispersants of the bis-type succinic imide include alkenylsuccinic imides and alkylsuccinic imides. These two bis-type succinic imides have a ratio xcex1/xcex2 of absorption peaks in an IR spectrum (wherein xcex1 is the intensity of an absorption peak at 1550xc2x110 cmxe2x88x921 and xcex2 is the intensity of an absorption peak at 1700xc2x110 cmxe2x88x921) of not more than 0.005, preferably not more than 0.003. When the ratio xcex1/xcex2 is in excess of 0.005, acid cannot be neutralized sufficiently.
As used herein, the intensity of an absorption peak refers to the height of the peak after the background has been subtracted.
Alkenylsuccinic imides are generally represented by the following formula (6): 
wherein each of R8 and R9, which may be identical to or different from each other, represents an alkenyl group having an average molecular weight of 200-4,000, preferably 500-3,000, more preferably 700-2,300, which are prepared from C2-C15 olefin polymers; each of R10 and R11, which may be identical to or different from each other, represents a C2-C5 alkenyl group, and n is an integer between 1 and 10 inclusive. The alkenyl groups R8 and R9 are preferably polyisobutenyl.
The bis-type alkenylsuccinic imides may be obtained by reacting polyisobutene or an ethylene-propylene copolymer with maleic anhydride, and then with polyamine. Examples of polyamines include monoalkylenediamines such as ethylenediamine, propylenediamine, butylenediamine, and pentylenediamine; and polyalkylene polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylene-hexamine, dibutylenetriamine, tributylenetetramine, and pentapentylenehexamine.
The bis-type imide alkyl succinates may be obtained by hydrogenation at the alkenyl groups R8 and R9 in formula (6) before or after the reaction with the aforementioned polyamine.
In the present invention, component (B) may be used singly or in combination. Component (B) is generally incorporated in an amount of 0.1-3% by weight, preferably 0.2-2% by weight, with respect to the total weight of the composition. Amounts less than 0.1% by weight may sometimes result in an insufficient acid neutralization effect obtainable from the synergism with component (A), whereas amounts in excess of 3% by weight may no longer produce appreciable effects commensurate with the amounts used.
The total base number of the composition of the present invention is preferably adjusted to fall within the range from 30 to 150 mgKOH/g, preferably 40 to 100 mgKOH/g (JIS K-2501; perchloric base method). Total acid numbers of less than 30 mgKOH/g may fail to neutralize acids perfectly, whereas total base numbers of higher than 150 mgKOH/g may increase the ash content in lube oil, raising the risk of producing great amounts of deposit during long-term use.
The concentration of all the nitrogen atoms of the composition of the present invention is preferably adjusted to fall within the range from 10 to 200 ppm, preferably from 20 to 100 ppm, on a weight basis. Total nitrogen atom concentrations of less than 10 ppm by weight may result in insufficient acid neutralization, whereas concentrations higher than 200 ppm by weight may easily form sludge during the process of degradation due to oxidation that may occur after prolonged use of the lube oil.
The composition of the present invention may be obtained by mixing the above-described components (A) and (B) with a lube oil base. Generally, in order to improve properties of a lube oil, additives such as antioxidants, viscosity index improvers, metal deactivating agents, pour point depressants, antiwear agents, antifoaming agents, and extreme pressure agents may also be incorporated. There is no particular limitation as to the additives that may be used, and a wide variety of conventionally employed additives may be used. Examples of antioxidants include, but are not limited to, amines such as alkylated diphenylamines, and phenyl-xcex1-naphthylamines; and phenol compounds such as 2,6-di-t-butyl phenol and 4,4xe2x80x2-methylenebis-(2,6-di-t-butyl phenol). These are used in amounts of 0.05-2% by weight with respect to the weight of the entirety of the composition. Examples of viscosity index improvers include, but are not limited to, polymethyl methacrylate, polyisobutylene, ethylene-propylene copolymers, styrene-isoprene copolymers, and styrene-butadiene hydrogenated copolymers. These are generally incorporated in amounts of 0.5-30% by weight with respect to the weight of the entirety of the composition. Examples of metal deactivating agents include benzotriazole, thiadiazole, and alkenylsuccinates. These are generally incorporated in amounts of 0.005-1% by weight with respect to the weight of the entirety of the composition. Examples of pour point depressants include polyalkyl methacrylate and polyalkylstyrene. These are generally used in amounts of 0.01-1% by weight with respect to the weight of the entirety of the composition. Examples of antiwear agents include organic molybdenum compounds such as MoDTP and MoDTC; organic zinc compounds such as ZnDTP, and organic boron compounds such as alkyl mercaptylborate, and solid lubricant-type antiwear agents such as graphite, molybdenum disulfide, antimony sulfide, boron compounds, and polytetrafluoroethylene. These are generally used in amounts of 0.1-3% by weight with respect to the weight of the entirety of the composition. Examples of antifoaming agents include dimethylpolysiloxane and polyacrylate, which are generally used in amounts of 0.0005-1% by weight with respect to the weight of the entirety of the composition. Examples of extreme pressure agents include sulfides of oils and fats, and diallyl disulfides. They are generally used in amounts of 0.1-15% by weight with respect to the weight of the entirety of the composition.